From the Family Guy episode "Family Gay" in which Peter buys a retarded horse and fills the refrigerator with the horse's sperm to begin breeding it. He reveals it to the family while Stewie eats his cereal. He first looks shocked, then narrows his eyes and continues eating....
(Look up "Milky Surprise" at Hulu for the clip)
If you end up with the awful result, you can then said to have gotten the "milky surprise" (taken from the name of the clip at Hulu).
Heather: "And four month's later how's that working out for ya'?"
Steve: "Well I've had more than a few milky surprises. Bitch be crazy."